According to the current state of the art, two persons are necessary to determine the length of an infant. The first person stretches the child out and the second person determines the length of the infant with a measuring tape.
Apart from the fact that two persons are always required for this measuring process, the measurement always presents a problem if the infant is in an incubator and every time the incubator is opened, it represents a significant stress for the child.
With the use of the measuring method described above, it is in fact unavoidable that the incubator has to be completely opened for measuring, since otherwise the measuring tape can not be laid out.